56,086 research outputs found
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Cerebral visual impairment captured with a structured history inventory in extremely preterm born children aged 6.5 years
No full textPurpose: To investigate whether a questionnaire can identify cerebral visual impairment (CVI) in a group of 6.5-year-old children born extremely preterm (EPT) as accurately as direct assessments. Methods: This prospective population-based study included 120 children born before 27 weeks' gestational age (66 males; mean, 25.4 ± 1.0 weeks) and 97 full-term controls (56 males; mean, 39.9 ± 1.1 weeks) at the age of 6.5 years, as part of the Extremely Preterm Infants in Sweden Study (EXPRESS). A questionnaire for detection of CVI was evaluated and compared with visual, perceptual, and cognitive assessments. Results: Parents of children born EPT reported more CVI features than the parents of control children, with median sum scores of 25 (95% CI, 18.1-31.9) and 11 (95% CI, 8.8-13.2), respectively (P < 0.001), and a median difference of 14 (95% CI, 6.6-21.4). Low rates of reported CVI features were significantly associated with better results from direct assessments within the EPT group and with less pronounced differences compared to controls. Conclusions: The questionnaire discriminated well between children born EPT and controls, and the scores were congruent with other evidence of visual, perceptual, and cognitive deficits. The easily used questionnaire compared favorably with direct assessment in identifying CVI in children born EPT and also provides valuable information to clinicians, and parents about the daily life problems associated with CVI
Clinical Effects of Faecal Microbiota Transplantation as Adjunctive Therapy in Dogs with Chronic Enteropathies—A Retrospective Case Series of 41 Dogs
No full textChronic enteropathies (CE) are common in dogs, but not all affected dogs respond to standard therapy. Successful responses to faecal microbial transplantation (FMT) in dogs with non-responsive CE have been reported in two case series. The objective of this retrospective study was to describe the clinical effects of FMT as an adjunctive therapy in a larger population of dogs with CE. Forty-one dogs aged 0.6–13.0 years (median 5.8) under treatment for CE at one referral animal hospital were included. Dogs were treated with 1–5 (median 3) FMTs as a rectal enema at a dose of 5–7 g/kg body weight. The canine inflammatory bowel disease activity index (CIBDAI) was compared at baseline versus after the last FMT. Stored faecal samples (n = 16) were analysed with the dysbiosis index. CIBDAI at baseline was 2–17 (median 6), which decreased to 1–9 (median 2; p < 0.0001) after FMT. Subsequently, 31/41 dogs responded to treatment, resulting in improved faecal quality and/or activity level in 24/41 and 24/41 dogs, respectively. The dysbiosis index at baseline was significantly lower for good responders versus poor responders (p = 0.043). Results suggest that FMT can be useful as an adjunctive therapy in dogs with poorly responsive CE
Energy dissipation and flux laws for unsteady turbulence
No full textDirect Numerical Simulations of spatially periodic unsteady turbulence show that the high Reynolds number scalings of the instantaneous energy dissipation rate and interscale energy flux at intermediate wavenumbers are qualitatively different from the well-known cornerstone scalings of equilibrium turbulence where and are time-dependent rms velocity and integral length-scales. Instead, they both scale as where and are length and velocity scales characterizing initial/overall unsteady turbulence conditions
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Real-space Manifestations of Bottlenecks in Turbulence Spectra
No full textAn energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence
Recent cases of falciparum malaria imported to Europe from Goa, India, December 2006-January 2007
No full textAn increase in numbers of malaria cases has recently been reported in travellers returning from India, in particular from the state of Goa, on the west coast. These cases have been reported to the European Network on Imported Infectious Disease Surveillance (TropNetEurop, http://www.tropnet.net). In the past two years, there have been no reports of malaria in European travellers to Goa. However, since late November 2006, the malaria surveillance map of the network has shownan unusually intensive signal from India, indicating an increase in the number of malaria reports from that region, including Goa. By 10 January, eight patients had been reported: two in Germany, four in Denmark, and two in Sweden. With the exception of two Danish cases, all patients travelled independently of one another. The two German patients, one of the Swedish patients and one of the Danish patients stayed in Goa for 2-3 weeks and had not visited other regions within India. No changes in the general recommendations for travellers have been made in Germany. In addition, the recent cluster of malaria cases imported from Goa has also prompted the Advisory Committee for Malaria Prevention in United Kingdom Travellers (ACMP) to issue temporary change to its recommendations. The ACMP advises that travel advisors should highlight the risk of malaria, instruct on the use of mosquito bite avoidance measures [6], and recommend malaria chemoprophylaxis to those travellers who will be visiting Goa, particularly areas north of Panaji, and who will be remote from medical care. This advice remains in effect until further notice as the situation is clarified. The recommended chemoprophylaxis is chloroquine plus proguanil. Alternatives are mefloquine, atovaquone plus proguanil, or doxycycline
Braid Entropy of Faraday Waves driven 2D Turbulence
No full textWe report new experimental results that use tools from braid theory to characterize two-dimensional turbulent flows driven by Faraday waves. The average topological length of the material fluid lines is found to grow exponentially with time. It allows us to compute the braid’s topological entropy SBraid. We show that SBraid increases as the square root of the turbulence kinetic energy E ~ u^2, where u^2 is the horizontal velocity variance . At long times, the PDFs of Lbraid are positively skewed and present strong exponential tails
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